Semi-continuous filaments including a crystalline polyolefin and a hydrocarbon tackifier resin, and process for making same

ABSTRACT

Nonwoven webs including one or more semi-continuous filaments made of a mixture including from about 50% w/w to about 99% w/w of at least one crystalline polyolefin (co)polymer, and from about 1% w/w to about 40% w/w of at least one hydrocarbon tackifier resin. The at least one semi-continuous filament exhibits molecular orientation, and at least one of the crystalline polyolefin (co)polymer or the nonwoven web exhibits a Heat of Fusion measured using Differential Scanning Calorimetry of greater than 50 Joules/g. A process for making the semi-continuous filaments and nonwoven webs is also disclosed.

TECHNICAL FIELD

The present disclosure relates to semi-continuous filaments including a crystalline polyolefin (co)polymer and a hydrocarbon tackifier resin, and more particularly, to nonwoven webs including such filaments, and methods for preparing such nonwoven webs.

BACKGROUND

Melt-spinning is a process for forming nonwoven webs of thermoplastic (co)polymeric filaments. In a typical melt-spinning process, one or more thermoplastic (co)polymer streams are extruded through a die containing one or more orifices and attenuated form micro-filaments, which are collected to form a melt-spun nonwoven web.

Thermoplastic (co)polymers commonly used in forming conventional melt-spun nonwoven webs include polyethylene (PE) and polypropylene (PP). Melt-spun nonwoven webs are used in a variety of applications, including acoustic and thermal insulation, filtration media, surgical drapes, and wipes, among others.

SUMMARY

Briefly, in one aspect, the present disclosure describes a nonwoven web including at least one semi-continuous filament including from about 50% w/w to about 99% w/w of at least one crystalline polyolefin (co)polymer, and from about 1% w/w to about 40% w/w of at least one hydrocarbon tackifier resin. The at least one semi-continuous filament exhibits molecular orientation, and the nonwoven web exhibits a Heat of Fusion measured using Differential Scanning Calorimetry of greater than 50 Joules/g. Preferably. the at least one semi-continuous filament comprises a plurality of melt-spun filaments. Preferably, the at least one semi-continuous filament is subjected to a filament bonding step before, during, or after collection, thereby forming a spun-bond web.

In some exemplary embodiments, the at least one crystalline polyolefin (co)polymer is selected from polyethylene, isotactic polypropylene, syndiotactic polypropylene, isotactic polybutylene, syndiotactic polybutylene, poly-4-methyl pentene), and mixtures thereof. In certain presently preferred embodiments, the at least one crystalline polyolefin (co)polymer exhibits a Heat of Fusion measured using Differential Scanning Calorimetry of greater than 50 Joules/g. In some such presently preferred embodiments, the at least one crystalline polyolefin (co)polymer is selected to be isotactic polypropylene, syndiotactic polypropylene, and mixtures thereof.

In certain exemplary embodiments, the at least one hydrocarbon tackifier resin is a saturated hydrocarbon. In certain presently preferred exemplary embodiments, the at least one hydrocarbon tackifier resin is selected from C₅ piperylene derivatives, C₉ resin oil derivatives, and mixtures thereof. In additional presently preferred exemplary embodiments, the at least one hydrocarbon tackifier resin makes up from 2% to 40% by weight of the (co)polymeric filaments, more preferably from 5% to 30% by weight of the (co)polymeric filaments, even more preferably from 7% to 20% by weight of the (co)polymeric filaments.

In certain exemplary embodiments, the filaments further include between about 0 to 30% w/w of at least one plasticizer. In some such embodiments, the at least one plasticizer is selected from oligomers of C₅ to C₁₄ olefins, and mixtures thereof.

In further presently preferred exemplary embodiments, the multiplicity of filaments exhibits a mean Actual Filament Diameter of less than 5 micrometers as determined using the Optical Microscopy Test as described herein. In other exemplary embodiments, the multiplicity of melt-spun filaments exhibits a mean Actual Filament Diameter of from about 1 micrometer to about 50 micrometers, inclusive; more preferably from 3 micrometers to 20 micrometers, inclusive; from 4 micrometers to 10 micrometers, inclusive; as determined using the Optical Microscopy Test described herein. 15.

In additional exemplary embodiments, the nonwoven web exhibits a Stiffness of at least 800 mg as measured using the Stiffness Test as described herein.

In another aspect, the present disclosure describes a process for making a nonwoven web made up of at least one semi-continuous filament, the process including heating a mixture of about 50% w/w to about 99% w/w of at least one crystalline polyolefin (co)polymer, and from about 1% w/w to about 40% w/w of at least one hydrocarbon tackifier resin to at least a Melting Temperature of the mixture to form a molten mixture, extruding the molten mixture through at least one orifice to form at least one semi-continuous filament, attenuating the at least one semi-continuous filament to draw and molecularly orient the at least one semi-continuous filament, and then cooling the at least one semi-continuous filament to a temperature below the Melting Temperature of the molten mixture to form a nonwoven web, The at least one semi-continuous filament exhibits molecular orientation, and at least one of the crystalline polyolefin (co)polymer or the nonwoven web exhibits a Heat of Fusion measured using Differential Scanning Calorimetry of greater than 50 Joules/g.

In further such exemplary embodiments, the at least one semi-continuous filament comprises a plurality of semi-continuous filaments, and the process further includes collecting the plurality of semi-continuous filaments as the nonwoven web on a collector. Preferably, the plurality of semi-continuous filaments is comprised of melt-spun filaments. Preferably the melt-spun filaments are subjected to a filament bonding step before, during, or after collection, thereby producing a spun-bond nonwoven web. In some such exemplary embodiments, the process further includes at least one of addition of a plurality of staple filaments to the plurality of semi-continuous filaments, or addition of a plurality of particulates to the plurality of semi-continuous filaments.

In some exemplary embodiments, the process further includes processing the collected nonwoven web using a process selected from autogenous bonding, through-air bonding, electret charging, embossing, needle-punching, needle tacking, hydroentangling, or a combination thereof.

Exemplary embodiments according to the present disclosure may have certain surprising and unexpected advantages over the art. One such advantage of exemplary embodiments of the present disclosure relates to increased tensile strength exhibited by the webs, even when prepared at low Basis Weight (i.e., less than or equal to 50 g/m², “gsm”). Increased tensile strength for low Basis Weight webs is important for many insulation applications, for example, thermal or acoustic insulation, more particularly acoustic or thermal insulation mats used in motor vehicles (e.g., aircraft, trains, automobiles, trucks, ships, and submersibles).

Thus, exemplary nonwoven webs as described herein may advantageously exhibit a Maximum Load in the Machine Direction Maximum Tensile Load in the Machine Direction as measured with the Tensile Strength Test as defined herein, of at least 40 Newtons (N), at least 50 N, at least 75 N, at least 100 N, at least 125 N, or even at least 150 N; and generally no greater than 1,000 N, 750 N, 500 N, or 250 N.

In other exemplary embodiments, the nonwoven webs as described herein may advantageously exhibit improved Stiffness, as evidenced by a Stiffness measured with the

Stiffness Test as defined herein, of at least 800 mg, 900 mg, 1,000 mg, 1500 mg, or even 2,000 mg; and generally no greater than 5,000 mg, 4,000 mg, 3,000 mg, or 2,500 mg.

In certain exemplary embodiments, the nonwoven webs exhibit a Basis Weight of from 1 g/m² (gsm) to 400 gsm, more preferably from 1 gsm to 200 gsm, even more preferably from 1 gsm to 100 gsm, or even 1 gsm to about 50 gsm.

Another advantage of exemplary embodiments relates to an increased ability to stretch the filaments by increasing the attenuation pressure without filament breakage, thus leading to higher filament spinning speeds and smaller diameter filaments. In some such embodiments, this may also advantageously limit or eliminate the possibility of newly formed filaments breaking and forming filament fragments ((i.e., “fly”) which can fall onto the collected nonwoven web and degrade the appearance of the web where they land.

An additional advantage of exemplary embodiments relates to an ability to use a higher melt temperature for the melt-spun process, which leads to a lower mean Actual Filament Diameter (AFD) of about 5 micrometers or less, and may even permit the production of sub-micrometer filaments (i.e., nanofilaments) having a mean Actual Filament Diameter (AFD) of less than one micrometer. Such nonwoven webs including sub-micrometer filaments achieve better acoustic and/or thermal insulation performance at equal or lower Basis Weight than comparable microfilament webs, thus leading to improved insulation performance at a lower production cost. Embodiments of the present disclosure may also exhibit higher production rates due to the lower melt viscosities achieved during melt-spinning of the filaments.

The following Listing of Exemplary Embodiments summarizes the various exemplary illustrative embodiments of the present disclosure.

Listing of Exemplary Embodiments

A. A nonwoven web, comprising:

at least one semi-continuous filament comprising from about 50% w/w to about 99% w/w of at least one crystalline polyolefin (co)polymer, and

from about 1% w/w to about 40% w/w of at least one hydrocarbon tackifier resin, wherein the at least one semi-continuous filament exhibits molecular orientation, and further wherein the melt-spun nonwoven web exhibits a Heat of Fusion measured using Differential Scanning Calorimetry of greater than 50 Joules/g.

B. The nonwoven web of Embodiment A or any following Embodiment, wherein the at least one crystalline polyolefin (co)polymer is selected from the group consisting of polyethylene, isotactic polypropylene, syndiotactic polypropylene, isotactic polybutylene, syndiotactic polybutylene, poly-4-methyl pentene, and mixtures thereof. C. The nonwoven web Embodiment B, wherein the at least one crystalline polyolefin (co)polymer exhibits a Heat of Fusion measured using Differential Scanning Calorimetry of greater than 50 Joules/g, D. The nonwoven web of any preceding or following Embodiment, wherein the at least one hydrocarbon tackifier resin is a saturated hydrocarbon. E. The nonwoven web of any preceding or following Embodiment, wherein the at least one hydrocarbon tackifier resin is selected from the group consisting of C₅ piperylene derivatives, C₉ resin oil derivatives, and mixtures thereof. F. The nonwoven web of any preceding or following Embodiment, wherein the at least one hydrocarbon tackifier resin makes up from 1% to 40% by weight of the (co)polymeric filaments. G. The nonwoven web of claim Embodiment F, wherein the at least one hydrocarbon tackifier resin makes up from 5% to 30% by weight of the (co)polymeric filaments. H. The nonwoven web of Embodiment G, wherein the at least one hydrocarbon tackifier resin makes up from 7% to 20% by weight of the (co)polymeric filaments. I. The nonwoven web of any preceding or following Embodiment, further comprising between about 0 to 30% of at least one plasticizer. J. The nonwoven web of Embodiment H, wherein the at least one plasticizer is selected from the group consisting of oligomers of C₅ to C₁₄ olefins, and mixtures thereof. K. The nonwoven web of any preceding or following Embodiment, wherein the nonwoven web exhibits a Maximum Load in the Machine Direction of at least 40 Newtons as measured using the Tensile Strength Test described herein. L. The nonwoven web of any preceding or following Embodiment, wherein the nonwoven web exhibits a Stiffness of at least 800 mg as measured using the Stiffness Test described herein. M. The melt-spun nonwoven web of any preceding or following Embodiment, wherein the nonwoven web exhibits a Basis Weight of 1 gsm to 400 gsm, preferably wherein the nonwoven web exhibits a Basis Weight of 1 gsm to 50 gsm. N. The melt-spun nonwoven web of any preceding Embodiment, wherein the plurality of (co)polymeric filaments exhibits a mean Actual Filament Diameter of less than five micrometers as determined using the Optical Microscopy Test described herein. O. The melt-spun nonwoven web of any one of Embodiments A-M, wherein the at least one (co)polymeric filament exhibits a mean Actual Filament Diameter of from about 4 micrometers to about 10 micrometers, inclusive, as determined using the Optical Microscopy Test described herein. P. A process for making a melt-spun nonwoven web, comprising:

a) heating a mixture of about 50% w/w to about 99% w/w of at least one crystalline polyolefin (co)polymer, and from about 1% w/w to about 40% w/w of at least one hydrocarbon tackifier resin to at least a Melting Temperature of the mixture to form a molten mixture;

b) extruding the molten mixture through at least one orifice to form at least one semi-continuous filament;

c) attenuating the at least one semi-continuous filament to draw and molecularly orient the at least one semi-continuous filament; and

d) cooling the at least one semi-continuous filament to a temperature below the Melting Temperature of the molten mixture to form a nonwoven web, wherein the at least one semi-continuous filament exhibits molecular orientation, and further wherein at least one of the crystalline polyolefin (co)polymer or the nonwoven web exhibits a Heat of Fusion measured using Differential Scanning Calorimetry of greater than 50 Joules/g.

Q. The process of Embodiment P, wherein extruding the mixture through at least one orifice to form the at least one semi-continuous filament is accomplished using a melt-spinning process. R. The process of Embodiment P or Q, further comprising at least one of addition of a plurality of staple filaments to the at least one semi-continuous filament, or addition of a plurality of particulates to the at least one semi-continuous filament. S. The process of any one of embodiments P, Q, or R, further comprising collecting the at least one semi-continuous filament as the melt-spun nonwoven web on a collector. T. The process of Embodiment S, further comprising processing the collected nonwoven web using a process selected from the group consisting of autogenous bonding, through-air bonding, electret charging, calendering, embossing, needle-punching, needle tacking, hydroentangling, or a combination thereof.

Various aspects and advantages of exemplary embodiments of the disclosure have been summarized. The above Summary is not intended to describe each illustrated embodiment or every implementation of the present certain exemplary embodiments of the present disclosure. The Detailed Description and Examples that follow more particularly exemplify certain presently preferred embodiments using the principles disclosed herein.

DETAILED DESCRIPTION

For the following Glossary of defined terms, these definitions shall be applied for the entire application, unless a different definition is provided in the claims or elsewhere in the specification.

Glossary

Certain terms are used throughout the description and the claims that, while for the most part are well known, may require some explanation. It should be understood that:

The terms “(co)polymer” or “(co)polymers” includes homopolymers and copolymers, as well as homopolymers or copolymers that may be formed in a miscible blend, e.g., by coextrusion or by reaction, including, e.g., transesterification. The term “copolymer” includes random, block and star (e.g. dendritic) copolymers.

The term “molecularly same (co)polymer” means one or more (co)polymers that have essentially the same repeating molecular unit, but which may differ in molecular weight, method of manufacture, commercial form, and the like.

The term “homogeneous” means exhibiting only a single phase of matter when observed at a macroscopic scale.

The term “Actual Filament Diameter” or “AFD” means the mean number diameter determined by measuring 20 individual filaments using the Optical Microscopy Test described herein.

The term “Effective Filament Diameter” or “EFD” means the apparent diameter of the filaments in a nonwoven web based on an air permeation test in which air at 1 atmosphere and room temperature is passed at a face velocity of 5.3 cm/sec through a web sample of known thickness, and the corresponding pressure drop is measured. Based on the measured pressure drop, the Effective Filament Diameter is calculated as set forth in Davies, C. N., The Separation of Airborne Dust and Particles, Institution of Mechanical Engineers, London Proceedings, 1B (1952).

The term “microfilaments” means a population of filaments having a mean AFD of at least one micrometer (μm) and preferably less than 1,000 μm.

The term “coarse microfilaments” means a population of microfilaments having a mean AFD of at least 10 μm and preferably less than or equal to 100 μm.

The term “fine microfilaments” means a population of microfilaments having a mean AFD of from one μm to 20 μm, inclusive.

The term “ultrafine microfilaments” means a population of microfilaments having a mean AFD of from one μm to 10 μm, inclusive.

The term “sub-micrometer filaments” means a population of filaments having a mean AFD of less than 1 μm.

The term “nanofilaments” means a population of filaments having a mean AFD of less than 1 μm.

The term “semi-continuous” with reference to a filament means that the filament is of finite but indeterminate length, the length of the filament being on the order of at least a factor of 1,000; 5,000; 10,000; 50,000; 100,000; or more times the Actual Fiber Diameter.

The terms “molecularly orient” and “molecular orientation” with reference to a single filament means that at least a substantial portion of the (co)polymer molecules making up the filament are aligned along the longitudinal axis of the filament.

The terms “particle” and “particulate” are used substantially interchangeably. Generally, a particle or particulate means a small distinct piece or individual part of a material in finely divided form. However, a particulate may also include a collection of individual particles associated or clustered together in finely divided form. Thus, individual particles used in certain exemplary embodiments of the present disclosure may clump, physically intermesh, electro-statically associate, or otherwise associate to form particulates. In certain instances, particulates in the form of agglomerates of individual particles may be intentionally formed such as those described in U.S. Pat. No. 5,332,426 (Tang et al.).

The term “nonwoven web” means a web characterized by entanglement or point bonding of at least one semi-continuous filament and preferably a plurality of semi-continuous filaments.

The term “composite nonwoven web” means a nonwoven web including at least one of a plurality of filaments and a plurality of particulates.

The term “particle-loaded nonwoven web” means a composite nonwoven web containing particles bonded to the filaments or enmeshed among the filaments, the particles optionally being absorbent and/or adsorbent.

The term “enmeshed” means that particles are distributed and physically held in the filaments of the web. Generally, there is point and line contact along the filaments and the particles so that nearly the full surface area of the particles is available for interaction with a fluid.

The term “self-supporting” with reference to a nonwoven web means a nonwoven web having sufficient coherency and strength so as to be drape-able and handle-able without substantial tearing or rupture.

The terms “melt-spinning” and “spun-bonding” mean processes for forming a nonwoven web by extruding a filament-forming material through one or more orifices to form at least one semi-continuous filament, attenuating the at least one semi-continuous filament by drawing the filament, and thereafter collecting a layer of the attenuated at least one semi-continuous filament, and, for spun-bonding, bonding the attenuated at least one semi-continuous filament before, during and/or after collection on a collector.

The term “die” means a processing assembly including one or more orifices for use in a process for extruding a molten (co)polymer mixture to form one or more semi-continuous filament(s), such process including but not limited to melt-spinning and/or spun-bonding processes.

The term “melt-spun filament(s)” means one or more semi-continuous filament(s) prepared using a melt-spinning process.

The term “spun-bond filaments(s)” means one or more semi-continuous filament(s) prepared using a melt-spinning process, wherein the one or more semi-continuous filament(s) are bonded together at one or more contact points along the surface(s) of the filament(s).

The term “calendering” means a process of passing a nonwoven web through rollers to obtain a compressed material. The rollers may optionally be heated, in which case bonding together of the components of the nonwoven web may be achieved.

The term “autogenous bonding” means bonding between filaments at an elevated temperature as obtained in an oven or with a through-air bonder without application of solid contact pressure such as in point-bonding or calendering.

The term “densification” means a process whereby filaments which have been deposited either directly or indirectly onto a filter winding arbor or mandrel are compressed, either before or after the deposition, and made to form an area, generally or locally, of lower porosity, whether by design or as an artifact of some process of handling the forming or formed filter. Densification also includes the process of calendering webs.

The term “machine direction” means the longitudinal direction in which a nonwoven web of indeterminate length is moved or wound onto a collector, and is distinguished from the “cross-web” direction, which is the lateral direction extending between the two lateral edges of the nonwoven web. Generally, the cross-web direction is orthogonal to the machine direction for a rectangular nonwoven web.

The term “Web Basis Weight” is calculated from the weight of a 10 cm×10 cm web sample.

The term “Web Thickness” is measured on a 10 cm×10 cm web sample using a thickness testing gauge having a tester foot with dimensions of 5 cm×12.5 cm at an applied pressure of 150 Pa.

The term “Polymer Density” is the mass per unit volume of the (co)polymer or (co)polymer blend that is used to form the nonwoven filaments of a nonwoven web. The Polymer Density for a (co)polymer may generally be found in the literature, and the Polymer Density of a (co)polymer blend may be calculated from the weighted average of the component (co)polymer Polymer Densities, based upon the weight percentages of the individual (co)polymers used to make up the (co)polymer blend. The Polymer Density of polypropylene resin is 0.91 g/cm³ and the Polymer Density of the hydrocarbon tackifier resins used herein is about 1.00 g/cm³. For the calculations of Solidity provided herein using the following formula, a Polymer Density of 0.91 g/cm³ was used.

The term “Solidity” is defined by the equation:

$\text{Solidity~~(\%)} = \frac{\left\lbrack {3.937*\text{Web~~Basis~~Weight}\left( {g\text{/}m^{2}} \right)} \right\rbrack}{\left\lbrack {\text{Web~~Thickness}({mils})*\text{Polymer~~Density}\left( {g\text{/}{cm}^{3}} \right)} \right\rbrack}$

wherein one mil is equivalent to 25 micrometers.

The term “Melting Temperature” as used herein, is the highest magnitude peak among principal and any secondary endothermic melting peaks in a cooling after first heating heat flow curve plotted as a function of temperature, as obtained using Differential Scanning Calorimetry (DSC).

The term “adjoining” with reference to a particular layer in a multi-layer nonwoven web means joined with or attached to another layer, in a position wherein the two layers are either next to (i.e., adjacent to) and directly contacting each other, or contiguous with each other but not in direct contact (i.e., there are one or more additional layers intervening between the layers).

The terms “about” or “approximately” with reference to a numerical value or a shape means +/− five percent of the numerical value or property or characteristic, but expressly includes the exact numerical value. For example, a viscosity of “about” 1 Pa-sec refers to a viscosity from 0.95 to 1.05 Pa-sec, but also expressly includes a viscosity of exactly 1 Pa-sec. Similarly, a perimeter that is “substantially square” is intended to describe a geometric shape having four lateral edges in which each lateral edge has a length which is from 95% to 105% of the length of any other lateral edge, but which also includes a geometric shape in which each lateral edge has exactly the same length.

The term “substantially” used with reference to a property or characteristic means that the property or characteristic is exhibited to a greater extent than the opposite of that property or characteristic is exhibited. For example, a substrate that is “substantially” transparent refers to a substrate that transmits more radiation (e.g. visible light) than it fails to transmit (e.g. absorbs and reflects). Thus, a substrate that transmits more than 50% of the visible light incident upon its surface is substantially transparent, but a substrate that transmits 50% or less of the visible light incident upon its surface is not substantially transparent.

By using terms of orientation such as “atop”, “on”, “over,” “covering”, “uppermost”, “underlying” and the like for the location of various elements in the disclosed coated articles, we refer to the relative position of an element with respect to a horizontally-disposed, upwardly-facing substrate. However, unless otherwise indicated, it is not intended that the substrate or articles should have any particular orientation in space during or after manufacture.

By using the term “overcoated” to describe the position of a layer with respect to a substrate or other element of an article of the present disclosure, we refer to the layer as being atop the substrate or other element, but not necessarily contiguous to either the substrate or the other element.

By using the term “separated by” to describe the position of a layer with respect to other layers, we refer to the layer as being positioned between two other layers but not necessarily contiguous to or adjacent to either layer.

As used in this specification and the appended embodiments, the singular forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to fine filaments containing “a compound” includes a mixture of two or more compounds. As used in this specification and the appended embodiments, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.

As used in this specification, the recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.8, 4, and 5).

Unless otherwise indicated, all numbers expressing quantities or ingredients, measurement of properties and so forth used in the specification and embodiments are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached listing of embodiments can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings of the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claimed embodiments, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

Various exemplary embodiments of the disclosure will now be described. Exemplary embodiments of the present disclosure may take on various modifications and alterations without departing from the spirit and scope of the disclosure. Accordingly, it is to be understood that the embodiments of the present disclosure are not to be limited to the following described exemplary embodiments, but are to be controlled by the limitations set forth in the claims and any equivalents thereof.

Nonwoven Melt-Spun (Spun-Bond) Fibrous Webs

In one exemplary embodiment, the disclosure describes a nonwoven web comprising at least one semi-continuous filament including from about 50% w/w to about 99% w/w of at least one crystalline polyolefin (co)polymer, and from about 1% w/w to about 40% w/w of at least one hydrocarbon tackifier resin, wherein the at least one semi-continuous filament exhibits molecular orientation, and further wherein the nonwoven web exhibits a Heat of Fusion measured using Differential Scanning Calorimetry of greater than 50 Joules/g.

In some exemplary embodiments, the nonwoven webs as described herein may advantageously exhibit improved tensile strength, as evidenced by a Maximum Tensile Load in the Machine Direction as measured with the Tensile Strength Test as defined herein, of at least 40 Newtons (N), at least 50 N, at least 75 N, at least 100 N, at least 125 N, or even at least 150 N; and generally no greater than 1,000 N, 750 N, 500 N, or 250 N.

In other exemplary embodiments, the nonwoven webs as described herein may advantageously exhibit improved Stiffness, as evidenced by a Stiffness measured with the Stiffness Test as defined herein, of at least 800 mg, 900 mg, 1,000 mg, 1500 mg, or even 2,000 mg; and generally no greater than 5,000 mg, 4,000 mg, 3,000 mg, or 2,500 mg.

Nonwoven Webs Including Semi-Continuous Filaments

Nonwoven webs of the present disclosure generally include one or more filaments that may be regarded as semi-continuous filaments. In some exemplary embodiments, the one or more semi-continuous filaments in the non-woven fibrous webs or composite webs comprise one or more microfilaments and may advantageously exhibit a mean Effective Filament Diameter (determined using the test method described below) of from about 5 micrometers to about 20 micrometers, inclusive; more preferably from about 7 micrometers to about 15 micrometers, inclusive, even more preferably from about 8 micrometers to about 10 micrometers, inclusive. In other exemplary embodiments, the semi-continuous filaments in the non-woven fibrous webs or composite webs may advantageously exhibit a mean Actual Filament Diameter (determined using the test method described below) of from about 1 micrometer to about 50 micrometers (μm), inclusive; more preferably from 3 μm to 20 μm, inclusive; even more preferably from about 4 μm to about 10 μm or even to about 9 μm, 8 μm, 7 μm, 6 μm, or even 5 μm, inclusive.

The nonwoven web may take a variety of forms, including mats, webs, sheets, scrims, fabrics, and a combination thereof.

Semi-Continuous Filament Components

Nonwoven webs of the present disclosure comprise semi-continuous filaments comprising from about 50% w/w to about 99% w/w of at least one crystalline polyolefin (co)polymer, and from about 1% w/w to about 40% w/w at least one hydrocarbon tackifier resin. In some embodiments, a single crystalline polyolefin (co)polymer) may be mixed with a single hydrocarbon tackifier resin. In other exemplary embodiments, a single crystalline polyolefin (co)polymer may be advantageously mixed with two or more hydrocarbon tackifier resins. In further exemplary embodiments, two or more crystalline polyolefin (co)polymers may be mixed with a single hydrocarbon tackifier resin. In other exemplary embodiments, two or more crystalline polyolefin (co)polymers may be advantageously mixed with two or more hydrocarbon tackifier resins.

Crystalline Polyolefin (Co)Polymer

The crystalline polyolefin (co)polymers useful in practicing embodiments of the present disclosure are generally crystalline polyolefin (co)polymers with a moderate level of crystallinity. Generally (co)polymer crystallinity arises from stereoregular sequences in the (co)polymer, for example stereoregular ethylene, propylene, or butylene sequences. For example, the (co)polymer can be: (A) a propylene homopolymer in which the stereoregularity is disrupted in some manner such as by regio-inversions; (B) a random propylene copolymer in which the propylene stereoregularity is disrupted at least in part by co-monomers; or (C) a combination of (A) and (B).

In some exemplary embodiments, the at least one crystalline polyolefin (co)polymer is selected from polyethylene, isotactic polypropylene, syndiotactic polypropylene, isotactic polybutylene, syndiotactic polybutylene, poly-4-methyl pentene, and mixtures thereof. The at least one crystalline polyolefin (co)polymer preferably exhibits a Heat of Fusion measured using Differential Scanning Calorimetry of greater than 50 Joules/g. In certain presently preferred exemplary embodiments, the at least one crystalline polyolefin (co)polymer is selected to be isotactic polypropylene, syndiotactic polypropylene, and mixtures thereof.

In some exemplary embodiments, the crystalline polyolefin (co)polymer is a (co)polymer that includes a non-conjugated diene monomer to aid in vulcanization and other chemical modification of the blend composition. The amount of diene present in the (co)polymer is preferably less than 10% by weight, and more preferably less than 5% by weight. The diene may be any non-conjugated diene which is commonly used for the vulcanization of ethylene propylene rubbers including, but not limited to, ethylidene norbornene, vinyl norbornene, and dicyclopentadiene.

In one exemplary embodiment, the crystalline polyolefin (co)polymer is a random copolymer of propylene and at least one co-monomer selected from ethylene, C₄-C₁₂ alpha-olefins, and combinations thereof. In one particular embodiment, the copolymer includes ethylene-derived units in an amount ranging from a lower limit of 2%, 5%, 6%, 8%, or 10% by weight to an upper limit of 20%, 25%, or 28% by weight. This embodiment also includes propylene-derived units present in the copolymer in an amount ranging from a lower limit of 72%, 75%, or 80% by weight to an upper limit of 98%, 95%, 94%, 92%, or 90% by weight. These percentages by weight are based on the total weight of the propylene and ethylene-derived units; i.e., based on the sum of weight percent propylene-derived units and weight percent ethylene-derived units being 100%.

In other exemplary embodiments, the crystalline polyolefin (co)polymer is a random propylene copolymer having a narrow compositional distribution. In certain presently preferred embodiments, the crystalline polyolefin (co)polymer is a random propylene copolymer exhibiting a Heat of Fusion determined using DSC of greater than 50 J/g.

The copolymer is described as random because for a copolymer comprising propylene, co-monomer, and optionally diene, the number and distribution of co-monomer residues is consistent with the random statistical polymerization of the monomers. In stereoblock structures, the number of block monomer residues of any one kind adjacent to one another is greater than predicted from a statistical distribution in random copolymers with a similar composition. Historical ethylene-propylene copolymers with stereoblock structure have a distribution of ethylene residues consistent with these blocky structures rather than a random statistical distribution of the monomer residues in the (co)polymer. The intramolecular composition distribution (i.e., randomness) of the copolymer may be determined by ¹³C NMR, which locates the co-monomer residues in relation to the neighboring propylene residues.

The crystallinity of the crystalline polyolefin (co)polymers may be expressed in terms of heat of fusion. Embodiments of the present disclosure include crystalline polyolefin (co)polymers exhibiting a heat of fusion as determined using differential scanning Calorimetry (DSC) greater than 50 J/g, greater than 51 J/g, greater than 55 J/g, greater than 60 J/g, greater than 70 J/g, greater than 80 J/g, greater than 90 J/g, greater than 100 J/g, or even about 110 J/g. Generally, the crystalline polyolefin (co)polymers exhibit a heat of fusion as determined using DSC less than 210 J/g, less than 200 J/g, less than 190 J/g, less than 180 J/g. less than 170 J/g. less than 160 J/g, less than 150 J/g, less than 140 J/g, less than 130 J/g, less than 120 J/g, less than 110 J/g, or even less than 100 J/g.

The level of crystallinity is also reflected in the Melting Point. In one embodiment of the present disclosure, the (co)polymer has a single Melting Point. Typically, a sample of propylene (co)polymer will show secondary melting peaks adjacent to the principal peak, which are considered together as a single Melting Point. The highest of these peaks is considered to be the Melting Point.

The crystalline polyolefin (co)polymer preferably has a melting point determined using DSC ranging from an upper limit of 300° C., 275° C., 250° C., 200° C., 175° C., 150° C., 125° C., 110° C., or even about 105° C., to a lower limit of about 105° C., 110° C., 120° C., 125° C., 130° C., 140° C., 150° C., 160° C., 175, 180° C., 190° C., 200° C., 225° C., or even about 250° C.

The crystalline polyolefin (co)polymers used in the disclosure generally have a weight average molecular weight (Mw) within the range having an upper limit of 5,000,000 Daltons (Da or g/mol), 1,000,000 Da, or 500,000 Da, and a lower limit of 10,000 Da, 20,000 Da, or 80,000 Da, and a molecular weight distribution W_(w)/W_(n) (MWD), sometimes referred to as a “polydispersity index” (PDI), ranging from a lower limit of 1.5, 1.8, or 2.0 to an upper limit of 40, 20, 10, 5, or 4.5. The M_(w) and MWD, as used herein, can be determined by a variety of methods, including those in U.S. Pat. No. 4,540,753 to Cozewith, et al., and references cited therein, such as those methods found in Verstrate et al., Macromolecules, v. 21, p. 3360 (1988), the descriptions of which are incorporated by reference herein for purposes of U.S. practices.

At least one crystalline polyolefin (co)polymer is generally present in an amount from about 50% w/w (50.0% w/w, 55% w/w, 60% w/w, 65% w/w, 70% w/w, 75% w/w, 80% w/w, 85% w/w, or even about 90% w/w) to about 99% w/w (99.0% w/w, 98% w/w 97% w/w, 96% w/w, 95% w/w, 90% w/w, 85% w/w, 80% w/w, 75% w/w, 70% w/w, 65% w/w, or even about 60% w/w) based on the total weight of the composition.

Hydrocarbon Tackifier Resins

Various types of natural and synthetic hydrocarbon tackifier resins, alone or in admixture with each other, can be used in preparing the filament compositions described herein, provided they meet the miscibility criteria described herein. Preferably, the hydrocarbon tackifier resin is selected to be miscible (i.e., forms a homogenous melt) with the crystalline polyolefin (co)polymer(s) when the mixture is in a molten state, that is, when the mixture of the at least one crystalline polyolefin (co)polymer and the at least one hydrocarbon tackifier resin is heated to a temperature at or above the Melting Temperature (as determined using DSC) of the mixture.

Suitable resins include, but are not limited to, natural rosins and rosin esters, hydrogenated rosins and hydrogenated rosin esters, coumarone-indene resins, petroleum resins, polyterpene resins, and terpene-phenolic resins. Specific examples of suitable petroleum resins include, but are not limited to aliphatic hydrocarbon tackifier resins, hydrogenated aliphatic hydrocarbon tackifier resins, mixed aliphatic and aromatic hydrocarbon tackifier resins, hydrogenated mixed aliphatic and aromatic hydrocarbon tackifier resins, cycloaliphatic hydrocarbon tackifier resins, hydrogenated cycloaliphatic resins, mixed cycloaliphatic and aromatic hydrocarbon tackifier resins, hydrogenated mixed cycloaliphatic and aromatic hydrocarbon tackifier resins, aromatic hydrocarbon tackifier resins, substituted aromatic hydrocarbons, and hydrogenated aromatic hydrocarbon tackifier resins.

As used herein, “hydrogenated” includes fully, substantially and at least partially hydrogenated resins. Suitable aromatic resins include aromatic modified aliphatic resins, aromatic modified cycloaliphatic resin, and hydrogenated aromatic hydrocarbon tackifier resins. Any of the above resins may be grafted with an unsaturated ester or anhydride to provide enhanced properties to the resin. Examples of grafted resins and their manufacture are described in the chapter titled Hydrocarbon Resins, Kirk-Othmer, Encyclopedia of Chemical Technology, 4th Ed. v. 13, pp. 717-743 (J. Wiley & Sons, 1995).

Hydrocarbon tackifier resins suitable for use as described herein include EMPR 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 116, 117, and 118 resins, OPPERA™ resins, and EMFR resins available from Exxon-Mobil Chemical Company (Spring, Tex.); ARKON™ P140, P125, P115, M115, and M135 and SUPER ESTER™ rosin esters available from Arakawa Chemical Company (Osaka, Japan); SYLVARES™ polyterpene resins, styrenated terpene resins and terpene phenolic resins, SYLVATAC™ and SYLVALITE™ rosin esters available from Arizona Chemical Company LLC (Jacksonville, Fla.); NORSOLENE™ aliphatic aromatic resins and WINGTACK™ C₅ resins available from TOTAL Cray Valley (Paris, France); DERTOPHENE™ terpene phenolic resins and DERCOLYTE™ polyterpene resins available from DRT Chemical Company (Dax Cedex, France); EASTOTAC™ resins, PICCOTAC™ resins, REGALITE™ and REGALREZ™ hydrogenated cycloaliphatic/aromatic resins available from Eastman Chemical Company (Kingsport, Tenn.); PICCOLYTE™ and PERMALYN™ polyterpene resins, rosins and rosin esters available from Pinova, Inc. (Brunswick, Ga.); coumerone/indene resins available from Neville Chemical Company (Pittsburg, Pa.); QUINTONE™ acid modified C₅ resins, C₅-C₉ resins, and acid modified C₅-C₉ resins available from Nippon Zeon (Tokyo, Japan); and CLEARON™ hydrogenated terpene resins available from Yasuhara Chemical Company, Ltd. (Tokyo, Japan). The preceding examples are illustrative only and by no means limiting.

In some exemplary embodiments, the hydrocarbon tackifier resin has a number average molecular weight (M_(n)) within the range having an upper limit of 5,000 Da, or 2,000 Da, or 1,000 Da, and a lower limit of 200 Da, or 400 Da, or 500 Da; a weight average molecular weight (M_(w)) ranging from 500 Da to 10,000 Da or 600 to 5,000 Da or 700 to 4,000 Da; a Z average molecular weight (M_(z)) ranging from 500 Da to 10,000 Da, and a polydispersity index (PDI) as measured by M_(w)/M_(n), of from 1.5 to 3.5, where M_(n), M_(w), and M_(z) are determined using size exclusion chromatography (SEC), or as provided by the supplier.

In other exemplary embodiments, the hydrocarbon tackifier resin has a lower molecular weight than the crystalline polyolefin (co)polymer.

The hydrocarbon tackifier resins of the present disclosure are generally selected to be miscible with the crystalline polyolefin (co)polymer in a molten state.

Hydrocarbon tackifier resins useful in embodiments of the present disclosure may have a softening point within the range having an upper limit of 180° C., 150° C., or 140° C., and a lower limit of 80° C., 120° C., or 125° C. Softening point (° C.) is measured using a ring and ball softening point device according to AS198 E-28 (Revision 1996).

Preferably, the hydrocarbon tackifier resin is a saturated hydrocarbon. In certain presently preferred exemplary embodiments, the hydrocarbon tackifier resin is selected from C₅ piperylene derivatives, C₉ resin oil derivatives, and mixtures thereof.

The hydrocarbon tackifier resin makes up from about 2% w/w (2.0% w/w, 3% w/w, 4% w/w, 5% w/w, 10% w/w, 15% w/w, 20% w/w) to about 40% (40.0% w/w, 35% w/w, 30% w/w, or even 25% w/w) based on the weight of the (co)polymeric filaments in the nonwoven web, more preferably from 5% to 30% by weight of the (co)polymeric filaments, even more preferably from 7% to 20% by weight of the (co)polymeric filaments.

Optional Nonwoven Web Components

In further exemplary embodiments, the nonwoven webs of the present disclosure may further comprise one or more optional components. The optional components may be used alone or in any combination suitable for the end-use application of the nonwoven webs. Three non-limiting, currently preferred optional components include optional electret filament components, optional non-melt-spun filament components, and optional particulate components as described further below.

Optional Plasticizer

In certain exemplary embodiments, the (co)polymeric filaments further include a plasticizer in an amount between about 0% to about 30% w/w of the filament composition, more preferably from 1% to 20% w/w, 1% to 10% w/w, 1% to 5%, or even 1% to 2.5%. In some such embodiments, the plasticizer is selected from oligomers of C₅ to C₁₄ olefins, and mixtures thereof. A non-limiting list of suitable commercially available plasticizers includes SHF and SUPEERSYN™ available from Exxon-Mobil Chemical Company (Houston, Tex.); STNFLUID™ available from Chevron-Phillips Chemical Co. (Pasadena, Tex.); DURASYN™ available from BP-Amoco Chemicals (London, England); NEXBASE™ available from Fortum Oil and Gas Co. (Espoo, Finland); SYNTON™ available from Crompton Corporation (Middlebury, Conn.); EMERY™ available from BASF GmbH (Ludwigshafen, Germany), formerly Cognis Corporation (Dayton, Ohio).

Optional Electret Fiber Component

The nonwoven webs of the present disclosure may optionally comprise electret filaments. Suitable electret filaments are described in U.S. Pat. Nos. 4,215,682; 5,641,555; 5,643,507; 5,658,640; 5,658,641; 6,420,024; 6,645,618, 6,849,329; and 7,691,168, the entire disclosures of which are incorporated herein by reference.

Suitable electret filaments may be produced by meltblowing filaments in an electric field, e.g. by melting a suitable dielectric material such as a (co)polymer or wax that contains polar molecules, passing the molten material through a melt-spinning die to form discrete filaments, and then allowing the molten (co)polymer to re-solidify while the discrete filaments are exposed to a powerful electrostatic field. Electret filaments may also be made by embedding excess charges into a highly insulating dielectric material such as a (co)polymer or wax, e.g. by means of an electron beam, a corona discharge, injection from an electron, electric breakdown across a gap or a dielectric barrier, and the like. Particularly suitable electret filaments are hydro-charged filaments.

Optional Non-Melt-Spun Fiber Component

In additional exemplary embodiments, the nonwoven web optionally further comprises a plurality of non-melt-spun filaments. Thus, in exemplary embodiments, the nonwoven web may additionally comprise discrete non-melt-spun filaments. Optionally, the discrete non-melt-spun filaments are staple filaments. Generally, the discrete non-melt-spun filaments act as filling filaments, e.g. to reduce the cost or improve the properties of the melt-spun nonwoven web.

Non-limiting examples of suitable non-melt-spun filling filaments include single component synthetic filaments, semi-synthetic filaments, polymeric filaments, metal filaments, carbon filaments, ceramic filaments, and natural filaments. Synthetic and/or semi-synthetic polymeric filaments include those made of polyester (e.g., polyethylene terephthalate), nylon (e.g., hexamethylene adipamide, polycaprolactam), polypropylene, acrylic (formed from a (co)polymer of acrylonitrile), rayon, cellulose acetate, polyvinylidene chloride-vinyl chloride copolymers, vinyl chloride-acrylonitrile copolymers, and the like.

Non-limiting examples of suitable metal filaments include filaments made from any metal or metal alloy, for example, iron, titanium, tungsten, platinum, copper, nickel, cobalt, and the like.

Non-limiting examples of suitable carbon filaments include graphite filaments, activated carbon filaments, poly(acrylonitrile)-derived carbon filaments, and the like.

Non-limiting examples of suitable ceramic filaments include any metal oxide, metal carbide, or metal nitride, including but not limited to silicon oxide, aluminum oxide, zirconium oxide, silicon carbide, tungsten carbide, silicon nitride, and the like.

Non-limiting examples of suitable natural filaments include those of bamboo, cotton, wool, jute, agave, sisal, coconut, soybean, hemp, and the like.

The filament component used may be virgin filaments or recycled waste filaments, for example, recycled filaments reclaimed from garment cuttings, carpet manufacturing, filament manufacturing, textile processing, or the like.

The size and amount of discrete non-melt-spun filling filaments, if included, used to form the nonwoven web, will generally depend on the desired properties (i.e., loftiness, openness, softness, drapability) of the nonwoven web 100 and the desired loading of the chemically active particulate. Generally, the larger the filament diameter, the larger the filament length, and the presence of a crimp in the filaments will result in a more open and lofty nonwoven article. Generally, small and shorter filaments will result in a more compact nonwoven article.

Optional Particulate Component

In certain exemplary embodiments, the nonwoven web further comprises a plurality of particulates. Exemplary nonwoven webs according to the present disclosure may advantageously include a plurality of chemically active particulates. The chemically active particulates can be any discrete particulate, which is a solid at room temperature, and which is capable of undergoing a chemical interaction with an external fluid phase. Exemplary chemical interactions include adsorption, absorption, chemical reaction, catalysis of a chemical reaction, dissolution, and the like.

Additionally, in any of the foregoing exemplary embodiments, the chemically active particulates may advantageously be selected from sorbent particulates (e.g. adsorbent particulates, absorbent particulates, and the like), desiccant particulates (e.g. particulates comprising a hygroscopic substance such as, for example, calcium chloride, calcium sulfate, and the like, that induces or sustains a state of dryness in its local vicinity), biocide particulates, microcapsules, and combinations thereof. In any of the foregoing embodiments, the chemically active particulates may be selected from activated carbon particulates, activated alumina particulates, silica gel particulates anion exchange resin particulates, cation exchange resin particulates, molecular sieve particulates, diatomaceous earth particulates, anti-microbial compound particulates, metal particulates, and combinations thereof.

In one exemplary embodiment of a nonwoven web particularly useful as a fluid filtration article, the chemically active particulates are sorbent particulates. A variety of sorbent particulates can be employed. Sorbent particulates include mineral particulates, synthetic particulates, natural sorbent particulates or a combination thereof. Desirably the sorbent particulates will be capable of absorbing or adsorbing gases, aerosols, or liquids expected to be present under the intended use conditions.

The sorbent particulates can be in any usable form including beads, flakes, granules or agglomerates. Preferred sorbent particulates include activated carbon; silica gel; activated alumina and other metal oxides; metal particulates (e.g., silver particulates) that can remove a component from a fluid by adsorption or chemical reaction; particulate catalytic agents such as hopcalite (which can catalyze the oxidation of carbon monoxide); clay and other minerals treated with acidic solutions such as acetic acid or alkaline solutions such as aqueous sodium hydroxide; ion exchange resins; molecular sieves and other zeolites; biocides; fungicides and virucides. Activated carbon and activated alumina are presently particularly preferred sorbent particulates. Mixtures of sorbent particulates can also be employed, e.g., to absorb mixtures of gases, although in practice to deal with mixtures of gases it may be better to fabricate a multilayer sheet article employing separate sorbent particulates in the individual layers.

In one exemplary embodiment of a nonwoven web particularly useful as a gas filtration article, the chemically active sorbent particulates are selected to be gas adsorbent or absorbent particulates. For example, gas adsorbent particulates may include activated carbon, charcoal, zeolites, molecular sieves, an acid gas adsorbent, an arsenic reduction material, an iodinated resin, and the like. For example, absorbent particulates may also include naturally porous particulate materials such as diatomaceous earth, clays, or synthetic particulate foams such as melamine, rubber, urethane, polyester, polyethylene, silicones, and cellulose. The absorbent particulates may also include superabsorbent particulates such as sodium polyacrylates, carboxymethyl cellulose, or granular polyvinyl alcohol.

In certain exemplary embodiments of a nonwoven web particularly useful as a liquid filtration article, the sorbent particulates comprise liquid an activated carbon, diatomaceous earth, an ion exchange resin (e.g. an anion exchange resin, a cation exchange resin, or combinations thereof), a molecular sieve, a metal ion exchange sorbent, an activated alumina, an antimicrobial compound, or combinations thereof. Certain exemplary embodiments provide that the web has a sorbent particulate density in the range of about 0.20 to about 0.5 g/cc.

Various sizes and amounts of sorbent chemically active particulates may be used to create a nonwoven web. In one exemplary embodiment, the sorbent particulates have a mean size greater than 1 mm in diameter. In another exemplary embodiment, the sorbent particulates have a mean size less than 1 cm in diameter. In further embodiments, a combination of particulate sizes can be used. In one exemplary additional embodiment, the sorbent particulates include a mixture of large particulates and small particulates.

The desired sorbent particulate size can vary a great deal and usually will be chosen based in part on the intended service conditions. As a general guide, sorbent particulates particularly useful for fluid filtration applications may vary in size from about 0.001 to about 3000 μm mean diameter. Generally, the sorbent particulates are from about 0.01 to about 1500 μm mean diameter, more generally from about 0.02 to about 750 μm mean diameter, and most generally from about 0.05 to about 300 μm mean diameter.

In certain exemplary embodiments, the sorbent particulates may comprise nano-particulates having a population mean diameter less than 1 μm. Porous nano-particulates may have the advantage of providing high surface area for sorption of contaminants from a fluid medium (e.g., absorption and/or adsorption). In such exemplary embodiments using ultrafine or nano-particulates, it may be preferred that the particulates are adhesively bonded to the filaments using an adhesive, for example a hot melt adhesive, and/or the application of heat to the melt-spun nonwoven web (i.e., thermal bonding).

Mixtures (e.g., bimodal mixtures) of sorbent particulates having different size ranges can also be employed, although in practice it may be better to fabricate a multilayer sheet article employing larger sorbent particulates in an upstream layer and smaller sorbent particulates in a downstream layer. At least 80 weight percent sorbent particulates, more generally at least 84 weight percent and most generally at least 90 weight percent sorbent particulates are enmeshed in the web. Expressed in terms of the web Basis Weight, the sorbent particulate loading level may for example be at least about 500 gsm for relatively fine (e.g. sub-micrometer-sized) sorbent particulates, and at least about 2,000 gsm for relatively coarse (e.g., micron-sized) sorbent particulates.

In some exemplary embodiments, the chemically active particulates are metal particulates. The metal particulates may be used to create a polishing nonwoven web. The metal particulates may be in the form of short filament or ribbon-like sections or may be in the form of grain-like particulates. The metal particulates can include any type of metal such as but not limited to silver (which has antibacterial/antimicrobial properties), copper (which has properties of an algaecide), or blends of one or more of chemically active metals.

In other exemplary embodiments, the chemically active particulates are solid biocides or antimicrobial agents. Examples of solid biocide and antimicrobial agents include halogen containing compounds such as sodium dichloroisocyanurate dihydrate, benzalkonium chloride, halogenated dialkylhydantoins, and triclosan.

In further exemplary embodiments, the chemically active particulates are microcapsules. Microcapsules are described in U.S. Pat. No. 3,516,941 (Matson), and include examples of the microcapsules that can be used as the chemically active particulates. The microcapsules may be loaded with solid or liquid biocides or antimicrobial agents. One of the main qualities of a microcapsule is that by means of mechanical stress the particulates can be broken in order to release the material contained within them. Therefore, during use of the nonwoven web, the microcapsules will be broken due to the pressure exerted on the nonwoven web, which will release the material contained within the microcapsule.

In certain such exemplary embodiments, it may be advantageous to use at least one particulate that has a surface that can be made adhesive or “sticky” so as to bond together the particulates to form a mesh or support nonwoven web for the filament component. In this regard, useful particulates may comprise a (co)polymer, for example, a thermoplastic (co)polymer, which may be in the form of semi-continuous filaments. Suitable polymers include polyolefins, particularly thermoplastic elastomers (TPE's) (e.g., VISTAMAXX™, available from Exxon-Mobil Chemical Company, Houston, Tex.). In further exemplary embodiments, particulates comprising a TPE, particularly as a surface layer or surface coating, may be preferred, as TPE's are generally somewhat tacky, which may assist bonding together of the particulates to form a three-dimensional network before addition of the filaments to form the nonwoven web. In certain exemplary embodiments, particulates comprising a VISTAMAXX™ TPE may offer improved resistance to harsh chemical environments, particularly at low pH (e.g., pH no greater than about 3) and high pH (e.g., pH of at least about 9) and in organic solvents.

Any suitable size or shape of particulate material may be selected. Suitable particulates may have a variety of physical forms (e.g., solid particulates, porous particulates, hollow bubbles, agglomerates, semi-continuous filaments, staple filaments, flakes, and the like); shapes (e.g., spherical, elliptical, polygonal, needle-like, and the like); shape uniformities (e.g., monodisperse, substantially uniform, non-uniform or irregular, and the like); composition (e.g. inorganic particulates, organic particulates, or combination thereof); and size (e.g., sub-micrometer-sized, micro-sized, and the like).

With particular reference to particulate size, in some exemplary embodiments, it may be desirable to control the size of a population of the particulates. In certain exemplary embodiments, particulates are physically entrained or trapped in the filament nonwoven web. In such embodiments, the population of particulates is generally selected to have a mean diameter of at least 50 μm, more generally at least 75 μm, still more generally at least 100 μm.

In other exemplary embodiments, it may be preferred to use finer particulates that are adhesively bonded to the filaments using an adhesive, for example a hot melt adhesive, and/or the application of heat to one or both of thermoplastic particulates or thermoplastic filaments (i.e., thermal bonding). In such embodiments, it is generally preferred that the particulates have a mean diameter of at least 25 μm, more generally at least 30 μm, most generally at least 40 μm. In some exemplary embodiments, the chemically active particulates have a mean size less than 1 cm in diameter. In other embodiments, the chemically active particulates have a mean size of less than 1 mm, more generally less than 25 micrometers, even more generally less than 10 micrometers.

However, in other exemplary embodiments in which both an adhesive and thermal bonding are used to adhere the particulates to the filaments, the particulates may comprise a population of sub-micrometer-sized particulates having a population mean diameter of less than one micrometer (μm), more generally less than about 0.9 μm, even more generally less than about 0.5 μm, most generally less than about 0.25 μm. Such sub-micrometer-sized particulates may be particularly useful in applications where high surface area and/or high absorbency and/or adsorbent capacity is desired. In further exemplary embodiments, the population of sub-micrometer-sized particulates has a population mean diameter of at least 0.001 μm, more generally at least about 0.01 μm, most generally at least about 0.1 μm, most generally at least about 0.2 μm.

In further exemplary embodiments, the particulates comprise a population of micro-sized particulates having a population mean diameter of at most about 2,000 μm, more generally at most about 1,000 μm, most generally at most about 500 μm. In other exemplary embodiments, the particulates comprise a population of micro-sized particulates having a population mean diameter of at most about 10 μm, more generally at most about 5 μm, even more generally at most about 2 μm (e.g., ultrafine micro-filaments).

Multiple types of particulates may also be used within a single finished web. Using multiple types of particulates, it may be possible to generate continuous particulate webs even if one of the particulate types does not bond with other particulates of the same type. An example of this type of system would be one where two types are particulates are used, one that bonds the particulates together (e.g., a semi-continuous polymeric filament particulate) and another that acts as an active particulate for the desired purpose of the web (e.g., a sorbent particulate such as activated carbon). Such exemplary embodiments may be particularly useful for fluid filtration applications.

Depending, for example, on the density of the chemically active particulate, size of the chemically active particulate, and/or desired attributes of the final nonwoven web article, a variety of different loadings of the chemically active particulates may be used relative to the total weight of the fibrous web. In one embodiment, the chemically active particulates comprise less than 90% wt. of the total nonwoven article weight. In one embodiment, the chemically active particulates comprise at least 10% wt. of the total nonwoven article weight.

In any of the foregoing embodiments, the chemically active particulates may be advantageously distributed throughout the entire thickness of the nonwoven web. However, in some of the foregoing embodiments, the chemically active particulates are preferentially distributed substantially on a major surface of the nonwoven web.

Furthermore, it is to be understood that any combination of one or more of the above described chemically active particulates may be used to form nonwoven webs according to the present disclosure.

Processes for Forming a Semi-Continuous Filament

In another aspect, the present disclosure describes a process for making a nonwoven web, comprising heating a mixture of about 50% w/w to about 99% w/w of a crystalline polyolefin (co)polymer, and from about 1% w/w to about 40% w/w of a hydrocarbon tackifier resin to at least a Melting Temperature of the mixture to form a molten mixture, extruding the molten mixture through at least one orifice to form at least one semi-continuous filament, attenuating the at least one semi-continuous filament to draw and molecularly orient the at least one semi-continuous filament, and cooling the at least one semi-continuous filament to a temperature below the Melting Temperature of the molten mixture to form a melt-spun nonwoven web, wherein the at least one semi-continuous (co)polymeric filament exhibits molecular orientation, and further wherein at least one of the crystalline polyolefin (co)polymer or the nonwoven web exhibits a Heat of Fusion measured using Differential Scanning Calorimetry of greater than 50 Joules/g.

In further such exemplary embodiments, the at least one semi-continuous filament comprises a plurality of semi-continuous filaments, and the process further includes collecting the plurality of semi-continuous filaments as the nonwoven web on a collector. Preferably, the plurality of semi-continuous filaments is comprised of melt-spun filaments. In the melt-spinning process, the crystalline polyolefin (co)polymer/hydrocarbon resin tackifier mixture is melted to form a molten mixture, which is then extruded through one or more orifices of a melt-spinning die.

Preferably the melt-spun filaments are subjected to a filament bonding step before, during, or after collection, thereby producing a spun-bond nonwoven web. In certain exemplary embodiments, bonding comprises one or more of autogenous thermal bonding, non-autogenous thermal bonding, through air bonding, and ultrasonic bonding.

Suitable melt-spinning and spun-bonding processes, attenuation methods and apparatus, and bonding methods and apparatus (including autogenous bonding methods) are described in U.S. Pat. Nos. 6,607,624 (Berrigan et al.) and 7,807,591 B2 (Fox et al.), the entire disclosures of which are incorporated herein by reference in their entireties.

In some exemplary embodiments, the process further includes at least one of addition of a plurality of staple filaments to the plurality of semi-continuous filaments, or addition of a plurality of particulates to the plurality of semi-continuous filaments.

In further embodiments, the process further includes processing the collected nonwoven web using a process selected from bonding, electret charging, embossing, needle-punching, needle tacking, hydroentangling, or a combination thereof.

In any of the foregoing processes, the melt-spinning should be performed within a range of temperatures hot enough to enable the crystalline polyolefin (co)polymer/hydrocarbon resin tackifier mixture to be melt-spun but not so hot as to cause unacceptable deterioration of the crystalline polyolefin (co)polymer/hydrocarbon resin tackifier mixture. For example, the melt-spinning can be performed at a temperature that causes the molten mixture of the crystalline polyolefin (co)polymer and hydrocarbon resin tackifier to reach a processing temperature at least 40-50° C. above the melting temperature.

Preferably, the processing temperature of the molten mixture is selected to be 200° C., 225° C., 250° C., 260° C., 270° C., 280° C., or even at least 290° C.; to less than or equal to about 360° C., 350° C., 340° C., 330° C., 320° C., 310° C., or even 300° C.

Processes for Forming Composite Nonwoven Webs

In some such exemplary embodiments, the process further includes at least one of addition of a plurality of staple filaments to the plurality of discrete, semi-continuous filaments, or addition of a plurality of particulates to the plurality of discrete, semi-continuous filaments, to form a composite nonwoven web.

In some exemplary embodiments, the method of making a composite nonwoven web comprises combining the microfilament or coarse microfilament population with the fine microfilament population, the ultrafine microfilament population, or the sub-micrometer filament population by mixing filament streams, hydroentangling, wet forming, plexifilament formation, or a combination thereof.

In combining the microfilament or coarse microfilament population with the fine, ultrafine or sub-micrometer filament populations, multiple streams of one or both types of filaments may be used, and the streams may be combined in any order. In this manner, nonwoven composite fibrous webs may be formed exhibiting various desired concentration gradients and/or layered structures.

For example, in certain exemplary embodiments, the population of fine, ultrafine or sub-micrometer filaments may be combined with the population of microfilaments or coarse microfilaments to form an inhomogenous mixture of filaments. In certain exemplary embodiments, at least a portion of the population of fine, ultrafine or sub-micrometer filaments is intermixed with at least a portion of the population of microfilaments. In other exemplary embodiments, the population of fine, ultrafine or sub-micrometer filaments may be formed as an overlayer on an underlayer comprising the population of microfilaments. In certain other exemplary embodiments, the population of microfilaments may be formed as an overlayer on an underlayer comprising the population of fine, ultrafine or sub-micrometer filaments.

Optional Particulate Loading Processes

In many applications, substantially uniform distribution of particles throughout the web is desired. There may also be instances where non-uniform distributions may be advantageous. In certain exemplary embodiments, a particulate density gradient may advantageously be created within the composite nonwoven web. For example, gradients through the depth of the web may create changes to the pore size distribution that could be used for depth filtration. Webs with a surface loading of particles could be formed into a filter where the fluid is exposed to the particles early in the flow path and the balance of the web provides a support structure and means to prevent sloughing of the particles. The flow path could also be reversed so the web can act as a pre-filter to remove some contaminants prior to the fluid reaching the active surface of the particles.

Various methods are known for adding a stream of particulates to a nonwoven filament stream. Suitable methods are described in U.S. Pat. Nos. 4,118,531 (Hauser), 6,872,311 (Koslow), and 6,494,974 (Riddell); and in U.S. Patent Application Publication Nos. 2005/0266760 (Chhabra and Isele), 2005/0287891 (Park) and 2006/0096911 (Brey et al.).

In other exemplary embodiments, the optional particulates could be added to a nonwoven filament stream by air laying a filament web, adding particulates to the filament web (e.g., by passing the web through a fluidized bed of particulates), optionally with post heating of the particulate-loaded web to bond the particulates to the filaments. Alternatively, a pre-formed web could be sprayed with a pre-formed dispersion of particulates in a volatile fluid (e.g. an organic solvent, or even water), optionally with post heating of the particulate-loaded web to remove the volatile fluid and bond the particulates to the filaments.

In further exemplary embodiments, the process further includes collecting the plurality of discrete, semi-continuous filaments as the nonwoven web on a collector. In certain such exemplary embodiments, the composite nonwoven web may be formed by depositing the population of fine, ultrafine or sub-micrometer filaments directly onto a collector surface, or onto an optional support layer on the collector surface, the support layer optionally comprising microfilaments, so as to form a population of fine, ultrafine or sub-micrometer filaments on the porous support layer.

The process may include a step wherein the optional support layer, which optionally may comprise polymeric microfilaments, is passed through a filament stream of fine, ultrafine or sub-micrometer filaments. While passing through the filament stream, fine, ultrafine or sub-micrometer filaments may be deposited onto the support layer so as to be temporarily or permanently bonded to the support layer. When the filaments are deposited onto the support layer, the filaments may optionally bond to one another, and may further harden while on the support layer.

In certain exemplary embodiments, the fine, ultrafine or sub-micrometer filament population is combined with an optional porous support layer that comprises at least a portion of the coarse microfilament population. In some exemplary embodiments, the microfilaments forming the porous support layer are compositionally the same as the population of microfilaments that forms the first layer. In other presently preferred embodiments, the fine, ultrafine or sub-micrometer filament population is combined with an optional porous support layer and subsequently combined with at least a portion of the coarse microfilament population. In certain other presently preferred embodiments, the porous support layer adjoins the second layer opposite the first layer.

In other exemplary embodiments, the porous support layer comprises a nonwoven fabric, a woven fabric, a knitted fabric, a foam layer, a screen, a porous film, a perforated film, an array of filaments, or a combination thereof. In some exemplary embodiments, the porous support layer comprises a thermoplastic mesh.

Optional Processing Steps

In some embodiments, the process further includes processing the collected nonwoven web using a process selected from bonding (e.g., autogenous bonding, through-air bonding, calendering, and the like), electret charging, embossing, needle-punching, needle tacking, hydroentangling, or a combination thereof.

Optional Bonding Processes

Depending on the condition of the filaments and the relative proportion of microfilaments and sub-micrometer filaments, some bonding may occur between the filaments themselves (e.g., autogenous bonding) and between the filaments and any optional particulates, before or during collection. “Bonding the filaments together” means adhering the filaments together firmly without an additional adhesive material, so that the filaments generally do not separate when the web is subjected to normal handling).

However, further bonding between the filaments themselves and between the filaments and any optional filaments or particulates in the collected web may be desirable to provide a matrix of desired coherency, making the web more handle-able and better able to hold any sub-micrometer filaments within the matrix (“bonding” filaments themselves means adhering the filaments together firmly, so they generally do not separate when the web is subjected to normal handling).

Bonding may be achieved, for example, using thermal bonding, adhesive bonding, powdered binder, hydroentangling, needle-punching, calendering, or a combination thereof. Conventional bonding techniques using heat and pressure applied in a point-bonding process or by smooth calender rolls can be used, though such processes may cause undesired deformation of filaments or excessive compaction of the web. A presently-preferred technique for bonding the filaments is through-air bonding as disclosed in U.S. Pat. Pub. No. 2008/0038976 (Berrigan et al.).

In some embodiments where light autogenous bonding provided by through-air bonding may not provide the desired web strength for peel or shear performance, it may be useful to incorporate a secondary or supplemental bonding step, for example, point bonding or calendering, after removal of the nonwoven web from the collector surface. Virtually any bonding technique may be used to achieve supplemental bonding, for example, application of one or more adhesives to one or more surfaces to be bonded, ultrasonic welding, or other thermal bonding methods able to form localized bond patterns, as known to those skilled in the art. Such supplemental bonding may make the web more easily handled and better able to hold its shape.

Optional Electret Charging Processes

In some particular embodiments, the melt-spun filaments may be advantageously electrostatically charged. Thus, in certain exemplary embodiments, the melt-spun filaments may be subjected to an electret charging process. An exemplary electret charging process is hydro-charging. Hydro-charging of filaments may be carried out using a variety of techniques including impinging, soaking or condensing a polar fluid onto the filament, followed by drying, so that the filament becomes charged. Representative patents describing hydro-charging include U.S. Pat. Nos. 5,496,507; 5,908,598; 6,375,886 B1; 6,406,657 B1; 6,454,986 and 6,743,464 B1. Preferably water is employed as the polar hydro-charging liquid, and the media preferably is exposed to the polar hydro-charging liquid using jets of the liquid or a stream of liquid droplets provided by any suitable spray means.

Devices useful for hydraulically entangling filaments are generally useful for carrying out hydro-charging, although the operation is carried out at lower pressures in hydro-charging than generally used in hydro-entangling. U.S. Pat. No. 5,496,507 describes an exemplary apparatus in which jets of water or a stream of water droplets are impinged upon the filaments in web form at a pressure sufficient to provide the subsequently-dried media with a filtration-enhancing electret charge.

The pressure necessary to achieve optimum results may vary depending on the type of sprayer used, the type of (co)polymer from which the filament is formed, the thickness and density of the web, and whether pretreatment such as corona charging was carried out before hydro-charging. Generally, pressures in the range of about 69 kPa to about 3450 kPa are suitable. Preferably, the water used to provide the water droplets is relatively pure. Distilled or deionized water is preferable to tap water.

The electret filaments may be subjected to other charging techniques in addition to or alternatively to hydro-charging, including electrostatic charging (e.g., as described in U.S. Pat. Nos. 4,215,682, 5,401,446 and 6,119,691), tribo-charging (e.g., as described in U.S. Pat. No. 4,798,850) or plasma fluorination (e.g., as described in U.S. Pat. No. 6,397,458 B1). Corona charging followed by hydro-charging and plasma fluorination followed by hydro-charging are particularly suitable charging techniques used in combination.

Optional Post-Collection Processing

Various processes conventionally used as adjuncts to filament-forming processes may be used in connection with filaments as they exit from one or more orifices of the belt blowing die. Such processes include spraying of finishes, adhesives or other materials onto the filaments, application of an electrostatic charge to the filaments, application of water mists to the filaments, and the like. In addition, various materials may be added to a collected web, including bonding agents, adhesives, finishes, and other webs or films. For example, prior to collection, extruded filaments or filaments may be subjected to a number of additional processing steps, e.g., further drawing, spraying, and the like. Various fluids may also be advantageously applied to the filaments before or during collection, including water sprayed onto the filaments, e.g., heated water or steam to heat the filaments, or cold water to quench the filaments.

After collection, the collected mass may additionally or alternatively be wound into a storage roll for later processing if desired. Generally, once the collected melt-spun nonwoven web has been collected, it may be conveyed to other apparatus such as calenders, embossing stations, laminators, cutters and the like; or it may be passed through drive rolls and wound into a storage roll.

Thus, in addition to the foregoing methods of making and optionally bonding or electret charging a nonwoven web, one or more of the following process steps may optionally be carried out on the web once formed:

(1) advancing the composite nonwoven web along a process pathway toward further processing operations;

(2) bringing one or more additional layers into contact with an outer surface of the sub-micrometer filament component, the microfilament component, and/or the optional support layer;

(3) calendering the composite nonwoven web;

(4) coating the composite nonwoven web with a surface treatment or other composition (e.g., a fire-retardant composition, an adhesive composition, or a print layer);

(5) attaching the composite nonwoven web to a cardboard or plastic tube;

(6) winding-up the composite nonwoven web in the form of a roll;

(7) slitting the composite nonwoven web to form two or more slit rolls and/or a plurality of slit sheets;

(8) placing the composite nonwoven web in a mold and molding the composite nonwoven web into a new shape; and

(9) applying a release liner over an exposed optional pressure-sensitive adhesive layer, when present.

Articles Incorporating Nonwoven Melt-Spun (Spun-Bond) Fibrous Webs

Nonwoven fibrous webs can be made using the foregoing processes. In some exemplary embodiments, the nonwoven web or composite web takes the form of a mat, web, sheet, a scrim, or a combination thereof.

In some particular exemplary embodiments, the nonwoven web or composite web may advantageously include charged melt-spun filaments, e.g., electret filaments. In certain exemplary embodiments, the melt-spun nonwoven web or web is porous. In some additional exemplary embodiments, the nonwoven web or composite web may advantageously be self-supporting. In further exemplary embodiments, the melt-spun nonwoven web or composite nonwoven web advantageously may be pleated, e.g., to form a filtration medium, such as a liquid (e.g., water) or gas (e.g., air) filter, a heating, ventilation or air conditioning (HVAC) filter, or a respirator for personal protection. For example, U.S. Pat. No. 6,740,137 discloses nonwoven webs used in a collapsible pleated filter element.

Webs of the present disclosure may be used by themselves, e.g., for filtration media, decorative fabric, or a protective or cover stock. Or they may be used in combination with other webs or structures, e.g., as a support for other fibrous layers deposited or laminated onto the web, as in a multilayer filtration media, or a substrate onto which a membrane may be cast. They may be processed after preparation as by passing them through smooth calendering rolls to form a smooth-surfaced web, or through shaping apparatus to form them into three-dimensional shapes.

A nonwoven web or composite web of the present disclosure can further comprise at least one or a plurality of other types of filaments (not shown) such as, for example, staple or otherwise semi-continuous filaments, melt spun continuous filaments or a combination thereof. The present exemplary fibrous webs can be formed, for example, into a non-woven web that can be wound about a tube or other core to form a roll, and either stored for subsequent processing or transferred directly to a further processing step. The web may also be cut into individual sheets or mats directly after the web is manufactured or sometime thereafter.

The melt-spun nonwoven webs or composite webs can be used to make any suitable article such as, for example, a thermal insulation article, an acoustic insulation article, a fluid filtration article, a wipe, a surgical drape, a wound dressing, a garment, a respirator, or a combination thereof. The thermal or acoustic insulation articles may be used as an insulation component for vehicles (e.g., trains, airplanes, automobiles and boats). Other articles such as, for example, bedding, shelters, tents, insulation, insulating articles, liquid and gas filters, wipes, garments, garment components, personal protective equipment, respirators, and the like, can also be made using melt-spun nonwoven webs of the present disclosure.

Flexible, drape-able and compact nonwoven webs may be preferred for certain applications, for examples as furnace filters or gas filtration respirators. Such nonwoven webs typically have a density greater than 75 kg/m³ and typically greater than 100 kg/m³ or even 120 kg/m³. However, open, lofty nonwoven webs suitable for use in certain fluid filtration applications generally have a maximum density of 60 kg/m³.

Thus, in certain exemplary embodiments, the nonwoven webs exhibit a Basis Weight of from 1 gsm to 400 gsm, more preferably from 1 gsm to 200 gsm, even more preferably from 1 gsm to 100 gsm, or even 1 gsm to about 50 gsm.

Certain presently-preferred nonwoven webs according to the present disclosure may have a Solidity less than 50%, 340%, 30%, 20%, or more preferably less than 15%, even more preferably less than 10%.

The operation of the processes of the present disclosure to produce nonwoven webs as described herein, will be further described with regard to the following detailed examples. These examples are offered to further illustrate the various specific and preferred embodiments and techniques. It should be understood, however, that many variations and modifications may be made while remaining within the scope of the present disclosure.

EXAMPLES

These Examples are merely for illustrative purposes and are not meant to be overly limiting on the scope of the appended claims. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the present disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

Summary of Materials

Unless otherwise noted, all parts, percentages, ratios, etc. in the Examples and the rest of the specification are by weight.

Mono-component polypropylene and blends of Polypropylene and OPPERA™ resins were used to prepare semi-continuous filaments comprising from about 50% w/w to about 99% w/w of at least one crystalline polyolefin (co)polymer, and from about 1% w/w to about 40% w/w of at least one hydrocarbon tackifier resin, as well as nonwoven webs including such semi-continuous filaments.

The crystalline polyolefin (co)polymer was selected as Total 3860 polypropylene (available from Total Petrochemicals and Refining U.S.A., Houston, Tex.).

The hydrocarbon tackifier resin was selected as OPPERA™ PR100A (available from Exxon-Mobil Chemical Co., Spring, Tex.)

Solvents and other reagents used may be obtained from Sigma-Aldrich Chemical Company (Milwaukee, Wis.).

Test Methods

The following test methods have been used in evaluating some of the Examples of the present disclosure.

Optical Microscopy Test of Actual Filament Diameter

The Actual Filament Diameter (AFD) was determined using an optical microscope equipped with a calibrated reticle. The AFD is the average (mean) number diameter determined from measurements taken on 20 individual filaments observed in the nonwoven web sample when positioned under the microscope objective at a focal point of the objective lens.

Effective Filament Diameter

The Effective Filament Diameter (EFD) was determined using an air flow rate of 32 L/min (corresponding to a face velocity of 5.3 cm/sec), using the method set forth in Davies, C. N., “The Separation of Airborne Dust and Particles,” Institution of Mechanical Engineers, London, Proceedings IB, 1952.

Differential Scanning Calorimetry (Melting Temperature and Heat of Fusion)

Differential Scanning Calorimetry (DSC) was used to determine the Melting Temperature and Heat of Fusion of the crystalline polyolefin, the mixture of the crystalline polyolefin with the hydrocarbon tackifier resin, and the nonwoven webs produced from the mixture.

The DSC analysis was carried out using a Model DSC Q2000 available from Ta Instruments Co. (New Castle, Del.). Approximately 1.5 mg to 10 mg of the crystalline polyolefin, the mixture of the crystalline polyolefin with the hydrocarbon tackifier resin, or the nonwoven web produced from the mixture, was loaded and sealed in an aluminum pan and placed in the DSC Q2000 apparatus.

DSC measurements on each sample was carried out using the following sequential

Heating-Cooling-Heating cycle. Each sample was initially heated from −20° C. to 250° C. (or at least 30° C. above the Melting Temperature of the sample) at a rate of 10° C./minute. Each sample was then held for 1 minute at 250° C., and then subsequently cooled down to −20° C. (or at least 50° C. below the crystallization temperature of the sample) at a rate of 20° C./min. Each sample was then held for 1 minute at −20° C. and then subsequently heated from −20° C. to 200° C. at 10° C./min.

The temperature corresponding to the highest-temperature endothermic peak was reported as the Melting Temperature (° C.), and the area under the same highest-temperature endothermic peak was reported as the Heat of Fusion.

Tensile Strength Test

The tensile properties of webs in the Examples were measured by pulling to failure a 1 inch by 6-inch sample (2.5 cm by 15.2 cm). The thickness of the nonwoven web samples was about 0.15 cm. The Tensile Strength Test was carried out using a commercially available tensile test apparatus designated as Instron Model 5544 (available from Instron Company, Canton, Mass.). The gauge length was 4 inches (10.2 cm), and the cross-head speed was 308 millimeters/per minute. The Maximum Tensile Load (in Newtons) was determined in the machine direction of the nonwoven web.

Stiffness Test

Stiffness of the nonwoven webs in the machine direction was measured with a Gurley Bending Resistance Tester Model 4171E (available from Gurley Precision Instruments, Inc., Troy, N.Y.). Five 1.5 inch (about 3.9 cm)×2 inch (about 5.1 cm) coupons were cut from the center lane of each nonwoven web with the 1.5 inch (about 3.9 cm) length corresponding to the machine direction of the web. Each coupon was then clamped in the Gurley Bending Resistance Tester, and the Tester motor was operated in each of two directions such that the Tester pendulum swung across the coupon until full deflection of the pendulum was achieved. Pendulum weights and positions were selected such that deflection of the pendulum was kept between 1 inch (2.54 cm) and 6 inches (about 15.2 cm) for any given sample. Results of nonwoven web Stiffness are reported for each nonwoven web as the average of the force (in mg) measured for each coupon from both directions.

Examples of Melt-Spun (Spun-Bond) Webs and Composite Melt-Spun (Spun-Bond) Webs

The following Examples illustrate the preparation of various melt-spun (spun-bond) nonwoven webs prepared according to the processes described in the present disclosure. For the Comparative Examples and Examples, melt-spun (spun-bond) filaments and nonwoven webs including such filaments were prepared using an apparatus as depicted in FIG. 1 of U.S. Pat. Nos. 6,607,624 (Berrigan et al.), and using the process as described generally by Berrigan et al. However, instead of two single-screw extruders (reference numeral 12 as shown in FIG. 1), a single 25 mm Berstorff twin-screw extruder (available from Krauss-Maffei Group, U.S.A., Florence, Ky.) was used to heat and extrude the molten (co)polymer mixture through the die.

Comparative Example C-1

Mono-component semi-continuous filaments and melt-spun (spun-bond) nonwoven webs including such filaments were prepared using Total 3860 polypropylene. The semi-continuous filaments were formed from a multi-orifice die that was 18″ (about 45.7 cm) wide and had approximately 1800 orifices. The semi-continuous filaments were extruded at 0.04 grams/orifice/minute (ghm) at a temperature of 245° C. The air attenuator was kept at 3 psig (about 20,684 Pa), which led to the calculated filament spinning speed of 837 m/min. The melt-spun (spun-bond) nonwoven web was made at a target basis weight of ˜120 gsm.

Comparative Example C-2

The melt-spun (spun-bond) web was made using the conditions which described in Comparative Example C-1, except the air pressure of the attenuator was increased to 7 psig (about 48,263 Pa). This was the point where considerable filament breakage was observed. The filament size of the melt-spun (spun-bond) media obtained was 6.2 μm at a calculated filament spinning speed of 1464 m/min.

Example 1

The melt-spun (spun-bond) media was made as described in Comparative Example C-2 except the 25 mm Berstorff twin-screw extruder was used with two loss in weight feeders to control the feeding of the Total PP 3860 and OPPERA PR100A resins to the extruder barrel and a melt pump to control the polymer melt flow to a die. The web was made using the blend ratio of (90/10) in between PP 3860 and OPPERA™ PR 100A. The extruder temperature was at about 245° C. and it delivered the blend melt stream to the melt-spun (spun-bond) die maintained at 245° C. The gear pump was adjusted so that a 0.04 grams/orifice/minute (ghm) polymer throughput rate was maintained at the melt-spun (spun-bond) die.

The resulting web was collected at the collector and had a basis weight of approximately 121 g/m². The air attenuator was kept at 3 psig (about 20,684 Pa) which led to a filament size of 8.3 microns at a calculated filament spinning speed of 817 m/min.

Example 2

The melt-spun (spun-bond) web was made using the conditions which described in Example 1, except the air pressure of the attenuator was increased to 18 psig (124,106 Pa). At this point no significant filament breakage occurred. The filament size of the melt-spun (spun-bond) media obtained was 4.6 μm at a calculated filament spinning speed of 2660 m/min.

Example 3

The melt-spun (spun-bond) web was made using the conditions which described in Example 2, except the flow rate of the blend was increased from 0.04 to 0.11 grams/orifice/minute. At this point no filament breakage was observed. The filament size of the melt-spun (spun-bond) media obtained was 7 μm at a calculated filament spinning speed of 3159 m/min.

Example 4

The melt-spun (spun-bond) web was made using the conditions which described in Example 1, except the ratio of PP 3860 and OPPERA™ PR 100A was increased to 80/20 w/w. The filament size of the melt-spun (spun-bond) media obtained was 7.3 μm at a calculated filament spinning speed of 1056 m/min.

Example 5

The melt-spun (spun-bond) web was made using the conditions which described in Example 4, except the air pressure of the attenuator was increased to 7 psig (about 48,263 Pa). The filament size of the melt-spun (spun-bond) media obtained was 6.6 μm at a calculated filament spinning speed of 1292 m/min.

Example 6

The melt-spun (spun-bond) web was made using the conditions which described in Example 5, except the air pressure of the attenuator was increased to 16 psig (110,316 Pa). The filament size of the melt-spun (spun-bond) media obtained was 5.2 μm at a calculated filament spinning speed of 2081 m/min.

Example 7

The melt-spun (spun-bond) web was made using the conditions which described in Example 6, except the flow rate of the blend was increased from 0.04 to 0.11 grams/orifice/minute and the air pressure of the attenuator was increased to 18 psig (124,106 Pa). The filament size of the melt-spun (spun-bond) media obtained was 7.5 μm at a calculated filament spinning speed of 2751 m/min.

Example 8

The melt-spun (spun-bond) web was made using the conditions which described in Example 7, except the air pressure of the attenuator was increased to 40 psig (275,790 Pa). The filament size of the melt-spun (spun-bond) media obtained was 6.1 μm at a calculated filament spinning speed of 4159 m/min.

The melt-spinning process conditions for Comparative Examples 1-2 and Examples 1-8 are summarized in Table 1, and the Melt-spun (Spun-bond) Nonwoven Web Properties for Comparative Examples 1-2 and Examples 1-8 are summarized in Table 2. Table 3 summarizes the DSC-measured Melting Temperatures and Heats of Fusion for each of the of melt-spun (spun-bond) nonwoven webs produced in Comparative Examples 1-2 and Examples 1-8.

TABLE 1 Melt-spinning Process Conditions for Comparative Examples 1-2 and Examples 1-8 Filament ΔP Attenuator Spinning Rate (at 85 L/m) Pressure Speed Example # Material (lb/hr) (mm H₂0) (psig) (m/min) C-1 PP 3860 10 6.3 3 837 C-2 PP 3860 10 8.42 7 1464 1 PP 3860 + 10 4.66 3 817 10% OPPERA 2 PP 3860 + 10 8.8 18 2660 10% OPPERA 3 PP 3860 + 25 5.8 18 3159 10% OPPERA 4 PP 3860 + 10 4.13 3 1056 20% OPPERA 5 PP 3860 + 10 7.07 7 1292 20% OPPERA 6 PP 3860 + 10 7.95 16 2081 20% OPPERA 7 PP 3860 + 25 4.9 18 2751 20% OPPERA 8 PP 3860 + 25 3.93 40 4159 20% OPPERA

TABLE 2 Melt-spun (Spun-bond) Nonwoven Web Properties for Comparative Examples 1-2 and Examples 1-8 Base Stiffness/ Tensile Strength Weight Thickness EFD AFD Stiffness Thickness MD CD Example # Material (gsm) (mils) (μm) (μm) (mg) (g/m) (N) (N) C-1 PP 3860 119 48 11.0 8.2 679.3 3.7 55.7 24.8 C-2 PP 3860 123 55.5 9.3 6.2 557 2.6 73.0 31.0 1 PP 3860 + 121 49 12.9 8.3 885.8 4.6 46.4 20.4 10% OPPERA 2 PP 3860 + 117 40 9.8 4.6 1316.5 8.4 143.6 39.8 10% OPPERA 3 PP 3860 + 122 37 13 7 1474.1 10.1 120.2 56.4 10% OPPERA 4 PP 3860 + 120 48.5 13.7 7.3 1514 7.9 70.4 35.2 20% OPPERA 5 PP 3860 + 122 50 10.5 6.6 1305.4 6.6 91.0 34.1 20% OPPERA 6 PP 3860 + 116 42 10.1 5.2 1292 7.8 124.8 45.2 20% OPPERA 7 PP 3860 + 124 41 13.8 7.5 1758.2 10.9 109.7 43.4 20% OPPERA 8 PP 3860 + 120 47 14.2 6.1 2091.2 11.3 147.4 69.6 20% OPPERA

TABLE 3 Melting Temperature and Heat of Fusion of melt-spun (spun-bond) webs described in Comparative Examples 1-2 and Examples 1-8 Melting Example Heat of Fusion Temperature Number Material (J/g) (° C.) C-1 PP 3860 102.6 162.8 C-2 PP 3860 103.6 163.2 1 PP 3860 + 96.3 160.8 10% OPPERA 2 PP 3860 + 90.1 163.3 10% OPPERA 3 PP 3860 + 88.5 163.5 10% OPPERA 4 PP 3860 + 97.7 159.7 20% OPPERA 5 PP 3860 + 84.4 160.4 20% OPPERA 6 PP 3860 + 83.4 161.1 20% OPPERA 7 PP 3860 + 81.1 161.8 20% OPPERA 8 PP 3860 + 87.3 162.3 20% OPPERA

The data provided in Tables 1 and 2 for Examples 1 & 2 and Comparative Examples C-1 and C-2 show that the addition of OPPERA™ PR 100A at 10 weight % enables one to increase the attenuator pressure from 7 psig (about 48,263 Pa) to 18 psig (124,106 Pa), thereby increasing the drawing of the filaments and thereby decreasing the Actual Filament Diameter without any filament breakage or “snapping” at a constant throughput. At the higher attenuator pressure, we were able to obtain filament sizes in the melt-spun (spun-bond) media of ˜4.6 microns at the same rate as for Comparative Example C-2, even though the filament spinning speed increases considerably, from 1464 to 2660 m/min, between Comparative Examples C-2 and Example 2. The stiffness/thickness ratio of the melt-spun (spun-bond) nonwoven web also increases from 3.59 to 4.59 comparing Comparative Example C-1 and Example 1 at the same attenuator pressure of 2 psig (about 13,790 Pa).

While not wishing to be bound by any particular theory, it appears that the addition of OPPERA™ PR 100A allows the filaments to be stretched and oriented more, as is evident from the filament spinning speed increase and decrease in filament size for Example 2 relative to Comparative Example C-2. This high orientation of the filament also leads to a considerable increase in the ratio of stiffness/thickness, which increases from 2.55 g/m to 8.36 g/m, as well as the tensile properties of the nonwoven web. In fact, the maximum tensile load to break in the machine direction (MD) doubles from 72.99N to 143.61N.

Furthermore, as can be seen from Tables 1 and 2, the addition of OPPERA™ PR 100A at 10 weight % helps to increase the throughput from 10 lbs/hr (about 4.55 kg/hr) to 25 lbs/hr (about 11.36 kg/hr), without a considerable change in the Actual Filament Diameter. Therefore, the OPPERA™ additive can be used to increase the throughput of the melt-spinning process without significantly altering the desired Actual Filament Diameter.

It was also observed that at higher throughput rates, the enhanced degree of molecular orientation in the filaments is even more evident from the increase in filament spinning speed from 1464 to 3159 m/min. This considerable increase in orientation also leads to an increase in the stiffness properties of the nonwoven web. As the stiffness/thickness ratio increases from 2.55 g/m to 10.12 g/m, which is a 4-fold increase in stiffness. The higher orientation of filaments at higher rates also leads to considerable increase in tensile properties as the maximum load (N) to break in MD increases from 72.99 N to 120.1 N.

Additionally, as can be seen from Table 1, Comparative Example C-1 and Examples 1 and 4 were all carried out at the same throughput and same attenuation pressure which leads to a similar filament spinning speed. However, the stiffness of the webs increases with increasing OPPERA™ PR 100A weight percentage. The ratio of stiffness to thickness increases from 3.59 g/m (0% OPPERA™ PR 100A) to 4.59 g/m (10% OPPERA™ PR 100A) to 7.93 g/m (20% OPPERA™ PR 100A).

Furthermore, by increasing the OPPERA™ PR 100A concentration to 20 weight %, we were able to increase the pressure of the attenuator to 40 psig (about 275,790 Pa) compared to 7 psig (about 48,263 Pa) for Comparative Example C-2. At that higher attenuator pressure, we still did not observe any significant filament breakage. Increasing the amount of OPPERA™ PR 100A thus leads to smaller Actual Filament Diameter and increased throughput ratek, because we can increase the attenuator pressure to draw the filaments more.

In fact, at 20 weight % OPPERA™ PR 100A, we were able to obtain filament diameters of 5.2 microns at a very high spinning speed of 4159 m/min compared to Comparative Example C-2. The stiffness/thickness ratio of the nonwoven web also increased from 2.55 to 11.30, and the maximum tensile load (N) to break in the machine direction (MD) of the nonwoven web increased from 72.99 N to 147.44 N.

Reference throughout this specification to “one embodiment,” “certain embodiments,” “one or more embodiments” or “an embodiment,” whether or not including the term “exemplary” preceding the term “embodiment,” means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the certain exemplary embodiments of the present disclosure. Thus, the appearances of the phrases such as “in one or more embodiments,” “in certain embodiments,” “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment of the certain exemplary embodiments of the present disclosure. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments.

While the specification has described in detail certain exemplary embodiments, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing, may readily conceive of alterations to, variations of, and equivalents to these embodiments. Accordingly, it should be understood that this disclosure is not to be unduly limited to the illustrative embodiments set forth hereinabove. In addition, all numbers used herein are assumed to be modified by the term “about.”

Furthermore, all publications and patents referenced herein are incorporated by reference in their entirety to the same extent as if each individual publication or patent was specifically and individually indicated to be incorporated by reference. Various exemplary embodiments have been described. These and other embodiments are within the scope of the following claims. 

1. A nonwoven web, comprising: at least one semi-continuous filament comprising from about 50% w/w to about 99% w/w of at least one crystalline polyolefin (co)polymer, and from about 1% w/w to about 40% w/w of at least one hydrocarbon tackifier resin, wherein the at least one semi-continuous (co)polymeric filament exhibits molecular orientation, and further wherein the nonwoven web exhibits a Heat of Fusion measured using Differential Scanning Calorimetry of greater than 50 Joules/g.
 2. The nonwoven web of claim 1, wherein the at least one crystalline polyolefin (co)polymer is selected from the group consisting of polyethylene, isotactic polypropylene, syndiotactic polypropylene, isotactic polybutylene, syndiotactic polybutylene, poly-4-methyl pentene, and mixtures thereof.
 3. The nonwoven web of claim 2, wherein the at least one crystalline polyolefin (co)polymer exhibits a Heat of Fusion measured greater than 50 Joules/g.
 4. The nonwoven web of claim 1, wherein the at least one hydrocarbon tackifier resin is a saturated hydrocarbon.
 5. The nonwoven web of claim 1, wherein the at least one hydrocarbon tackifier resin is selected from the group consisting of C₅ piperylene derivatives, C₉ resin oil derivatives, and mixtures thereof.
 6. The nonwoven web of claim 1, wherein the at least one hydrocarbon tackifier resin makes up from 2% to 40% by weight of the (co)polymeric filaments.
 7. The nonwoven web of claim 6, wherein the at least one hydrocarbon tackifier resin makes up from 5% to 30% by weight of the (co)polymeric filaments.
 8. The nonwoven web of claim 7, wherein the at least one hydrocarbon tackifier resin makes up from 7% to 20% by weight of the (co)polymeric filaments.
 9. The nonwoven web of claim 1, wherein the at least one (co)polymeric filament exhibits a mean Actual Filament Diameter of less than 5 micrometers as determined using the Optical Microscopy Test.
 10. The nonwoven web of claim 1, wherein the at least one (co)polymeric filament exhibits a mean Actual Filament Diameter of from about 4 micrometers to about 10 micrometers, inclusive, as determined using the Optical Microscopy Test.
 11. The nonwoven web of claim 1, further comprising between 0 to about 30% of at least one plasticizer.
 12. The nonwoven web of claim 11, wherein the at least one plasticizer is selected from the group consisting of oligomers of C₅ to C₁₄ olefins, and mixtures thereof.
 13. The nonwoven web of claim 1, wherein the nonwoven web exhibits a Maximum Load in the Machine Direction of at least 40 Newtons as measured using the Tensile Strength Test.
 14. The nonwoven web of claim 1, wherein the nonwoven web exhibits a Basis Weight of from 1 gsm to 400 gsm, inclusive, optionally wherein the Basis Weight is from 1 gsm to 50 gsm.
 15. The nonwoven web of claim 1, wherein the nonwoven web exhibits a Stiffness of at least 800 mg as measured using the Stiffness Test.
 16. A process for making a nonwoven web, comprising: a) heating a mixture of about 50% w/w to about 99% w/w of at least one crystalline polyolefin (co)polymer, and from about 1% w/w to about 40% w/w of at least one hydrocarbon tackifier resin to at least a Melting Temperature of the mixture to form a molten mixture; b) extruding the molten mixture through at least one orifice to form at least one semi-continuous filament; c) attenuating the at least one semi-continuous filament to draw and molecularly orient the at least one semi-continuous filament; and d) cooling the at least one semi-continuous filament to a temperature below the Melting Temperature of the molten mixture to form a nonwoven web, wherein the at least one semi-continuous (co)polymeric filament exhibits molecular orientation, and further wherein at least one of the crystalline polyolefin (co)polymer or the nonwoven web exhibits a Heat of Fusion measured using Differential Scanning Calorimetry of greater than 50 Joules/g.
 17. The process of claim 16, wherein extruding the mixture through at least one orifice to form the at least one semi-continuous filament is accomplished using a melt-spinning process.
 18. The process of claim 16, further comprising at least one of addition of a plurality of staple filaments to the at least one semi-continuous filament, or addition of a plurality of particulates to the at least one semi-continuous filament.
 19. The process of claim 16, further comprising collecting the at least one semi-continuous filament as the nonwoven web on a collector.
 20. The process of claim 19, further comprising processing the collected nonwoven web using a process selected from the group consisting of autogenous bonding, through-air bonding, electret charging, calendering, embossing, needle-punching, needle tacking, hydroentangling, or a combination thereof. 